The present invention relates to a hydraulic brake system for automotive vehicles, comprising a master brake cylinder including a supply chamber connectible to a non-pressurized reservoir, and a working chamber in communication with a brake line leading to pressure control valves of a brake slip control device coupled to which is at least one wheel brake.
During operation of the brake slip control device, in brake systems of the afore-described type, the repeated actuation of the wheel brake after a pressure relief requires a pressure fluid amount largely exceeding the supply capacity of the master brake cylinder in an actuating process. It is, therefore, necessary that, during operation of the brake slip control device, pressure fluid from an additional pressure fluid source, for example, an electronically operated energy supply system independent of the master brake cylinder, be supplied to the wheel brake. Moreover, it is necessary for the master brake cylinder, during operation of the brake slip control device, to be kept in an actuating position which, upon failure of the brake control device or the energy supply system, will safeguard operation of the wheel brake until standstill of the vehicle.
In a conventional brake system as disclosed, for example, by DE-OS No. 30 40 562 wherein, for actuating the master brake cylinder, a brake force booster energized by a hydraulic energy supply system is provided, the supply chamber of the master brake cylinder, by way of an electromagnetically operable control valve of the brake slip control device and a hydraulically controllable valve unit coupled to the control valve, is connectible to the booster chamber of the brake force booster in order to supply, during operation of the brake slip control device, the wheel brake cylinders in communication with the working chamber with pressure fluid from the energy supply system of the brake force booster, by way of the supply chamber, the piston sleeve and the working chamber of the master brake cylinder. Moreover, a positioning piston is provided, in the prior brake system, in the supply chamber of the master brake cylinder, which positioning piston, upon a pressure being applied to the supply chamber, is movable toward a housing stop to keep the master cylinder piston in a ready-for-operation condition thereby safeguarding an operation of the brake in the event of a failure or defective condition of the energy supply or the brake slip control. The above configuration of the brake system involves the disadvantage that it is applicable only in connection with a hydraulic brake force booster through which the pressure supplied to the supply chamber of the master brake cylinder is controlled in proportion to the exerted actuating force. Also, it is a disadvantage of the prior brake system that the serviceability of the hydraulic brake force booster and that of the brake slip control device are dependent of one another. Moreover, the prior art brake system is relatively complex and costly thus being unsuitable for use with vehicles of a lower price category.
It is an object of the present invention to provide, in a brake system of the afore-mentioned type, an additional energy supply for the operation of the brake slip control device independent of the actuating system of the master brake cylinder and exhibiting low construction cost.